Method and apparatus for wireless communication

ABSTRACT

Operations of a UE and eNB are provided when there is a cell which can perform cell on/off. In this case, the UE may performs receiving signal on downlink channel and processing with the signal on the downlink channel. In addition, the signal on the downlink channel may includes a discovery signal when the cell is off-state, and the discovery signal is a signal used for cell identification and/or measurement.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2014/010216, filed on Oct. 28, 2014, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application Nos. 61/896,630,filed on Oct. 28, 2013, 61/925,194, filed on Jan. 8, 2014, 62/035,357,filed on Aug. 8, 2014 and 62/054,985, filed on Sep. 25, 2014, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

This invention relates to wireless communication, more specifically totechniques for performing cell on/off.

BACKGROUND ART

3rd generation partnership project (3GPP) long term evolution (LTE) isan improved version of a universal mobile telecommunication system(UMTS) and a 3GPP release 8. The 3GPP LTE uses orthogonal frequencydivision multiple access (OFDMA) in a downlink, and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink. The3GPP LTE employs multiple input multiple output (MIMO) having up to fourantennas. In recent years, there is an ongoing discussion on 3GPPLTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.

The commercialization of the 3GPP LTE (A) system is being recentlyaccelerated. The LTE systems are spread more quickly as respond tousers' demand for services that may support higher quality and highercapacity while ensuring mobility, as well as voice services. The LTEsystem provides for low transmission delay, high transmission rate andsystem capacity, and enhanced coverage.

To increase the capacity for the users' demand of services, increasingthe bandwidth may be essential, a carrier aggregation (CA) technology orresource aggregation over intra-node carriers or inter-node carriersaiming at obtaining an effect, as if a logically wider band is used, bygrouping a plurality of physically non-continuous bands in a frequencydomain has been developed to effectively use fragmented small bands.Individual unit carriers grouped by carrier aggregation is known as acomponent carrier (CC). For inter-node resource aggregation, for eachnode, carrier group (CG) can be established where one CG can havemultiple CCs. Each CC is defined by a single bandwidth and a centerfrequency.

Recently, in addition to carriers in licensed band, carriers inunlicensed band are also considered for carrier aggregation. In thiscase, a UE can be configured with zero or more carriers in licensed bandand zero or more carriers in unlicensed band. Due to its nature ofunlicensed band where the medium is shared by multiple devices and thuscontinuous transmission is not easily feasible, it is very natural toassume that discontinuous transmission from an eNB operating inunlicensed band. The inventions embodied in this application are appliedto carriers in unlicensed band

A system in which data is transmitted and/or received in a broadbandthrough a plurality of CCs is referred to as a multi-component carriersystem (multi-CC system) or a CA environment. A system in which data istransmitted and/or received in a broadband through a plurality of CGs isreferred to as a inter-node resource aggregation or dual connectivityenvironment. The multi-component carrier system and dual connectivitysystem perform both a narrow band and a broad band by using one or morecarriers. For example, when an each carrier corresponds to a bandwidthof 20 MHz, a bandwidth of a maximum of 100 MHz may be supported by usingfive carriers.

In this circumstances, different types of cells are used for enhance theperformance of wireless communication. For example, user equipment cantransmits/receives signals with a plurality of eNB. In this case,network synchronization needs to be considered to enhance channelquality, etc.

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide method and apparatusfor effectively performing wireless communication under variouscircumstances. An another object of the present invention is to providemethod and apparatus for receiving and/or transmitting signals whenthere is a cell which can perform cell on-off.

Another object of the present invention is to provide method andapparatus for processing such as measurement when there is a cell whichcan perform cell on-off.

Solution to Problem

An example of the present invention(s) in this application is a methodfor wireless communication by a user equipment (UE) with on-offavailable or discontinuously transmitting cell. The method may comprisereceiving signal on downlink channel and processing with the signal onthe downlink channel, wherein the signal on the downlink channelincludes a discovery signal when the cell is off-state, and wherein thediscovery signal is a signal used for cell identification and/ormeasurement.

Another example of the present invention(s) in this application is auser equipment for wireless communication with on-off available cell.The UE may comprise a radio frequency (RF) unit for transmitting andreceiving a signal, and a processor operatively coupled to the RF unit,wherein the processor is configured for transmitting a signal via the RFunit, wherein the processor receives a signal on downlink channelincluding a discovery signal when the cell is off-state, and wherein thediscovery signal is a signal used for cell identification and/ormeasurement.

Advantageous Effects of Invention

According to the present invention, a UE and a eNB perform effectivelywireless communication under various circumstances including carriersoperated in unlicensed band. According to the present invention, a UEand a eNB perform efficiently receiving and/or transmitting signals whenthe eNB can perform cell on-off.

According to the present invention, a UE performs effectively processingsuch as measurement when there is a cell which can perform cell on-off.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 shows an exemplary concept for a carrier aggregation (CA)technology according to an exemplary embodiment of the presentinvention.

FIG. 3 shows a structure of a radio frame to which the present inventionis applied.

FIG. 4 shows downlink control channels to which the present invention isapplied.

FIG. 5 shows an example of dual connectivity to a macro cell and a smallcell.

FIG. 6 shows an example of a protocol architecture supporting dualconnectivity.

FIG. 7 describes an example of case that transmissions of PCell andSCell according to the present invention.

FIG. 8 is a flowchart briefly describing an example of operation of a UEaccording to the invention(s) in this application.

FIG. 9 is a flowchart briefly describing an example of operation of aeNB (BS) according to the invention(s) in this application.

FIG. 10 is a block diagram which briefly describes a wirelesscommunication system.

MODE FOR THE INVENTION

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also bereferred to as an evolved-UMTS terrestrial radio access network(E-UTRAN) or a long term evolution (LTE)/LTE-A system.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to an user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, a cell, node-B, or nodeetc.

Multi-access schemes applied to the wireless communication system arenot limited. Namely, various multi-access schemes such as CDMA (CodeDivision Multiple Access), TDMA (Time Division Multiple Access), FDMA(Frequency Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier-FDMA), OFDM-FDMA,OFDM-TDMA, OFDM-CDMA, or the like, may be used. For uplink transmissionand downlink transmission, a TDD (Time Division Duplex) scheme in whichtransmission is made by using a different time or an FDD (FrequencyDivision Duplex) scheme in which transmission is made by using differentfrequencies may be used.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

More details, radio protocol architecture for a user plane (U-plane) anda control plane (C-plane) are explained. A PHY layer provides an upperlayer with an information transfer service through a physical channel.The PHY layer is connected to a medium access control (MAC) layer whichis an upper layer of the PHY layer through a transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. The transport channel is classified according to howand with what characteristics data is transferred through a radiointerface. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data are transferred throughthe physical channel. The physical channel may be modulated using anorthogonal frequency division multiplexing (OFDM) scheme, and mayutilize time and frequency as a radio resource.

Functions of the MAC layer include mapping between a logical channel anda transport channel and multiplexing/de-multiplexing on a transportblock provided to a physical channel over a transport channel of a MACservice data unit (SDU) belonging to the logical channel. The MAC layerprovides a service to a radio link control (RLC) layer through thelogical channel.

Functions of the RLC layer include RLC SDU concatenation, segmentation,and reassembly. To ensure a variety of quality of service (QoS) requiredby a radio bearer (RB), the RLC layer provides three operation modes,i.e., a transparent mode (TM), an unacknowledged mode (UM), and anacknowledged mode (AM). The AM RLC provides error correction by using anautomatic repeat request (ARQ).

Functions of a packet data convergence protocol (PDCP) layer in the userplane include user data delivery, header compression, and ciphering.Functions of a PDCP layer in the control plane include control-planedata delivery and ciphering/integrity protection.

A radio resource control (RRC) layer is defined only in the controlplane. The RRC layer serves to control the logical channel, thetransport channel and the physical channel in association withconfiguration, reconfiguration and release of radio bearers (RBs). An RBis a logical path provided by the first layer (i.e., the PHY layer) andthe second layer (i.e., the MAC layer, the RLC layer, and the PDCPlayer) for data delivery between the UE and the network.

The setup of the RB implies a process for specifying a radio protocollayer and channel properties to provide a particular service and fordetermining respective detailed parameters and operations. The RB can beclassified into two types, i.e., a signaling RB (SRB) and a data RB(DRB). The SRB is used as a path for transmitting an RRC message in thecontrol plane. The DRB is used as a path for transmitting user data inthe user plane.

When an RRC connection is established between an RRC layer of the UE andan RRC layer of the network, the UE is in an RRC connected state (it mayalso be referred to as an RRC connected mode), and otherwise the UE isin an RRC idle state (it may also be referred to as an RRC idle mode).

FIG. 2 shows an exemplary concept for a carrier aggregation (CA)technology according to an exemplary embodiment of the presentinvention.

Referring to FIG. 2, the downlink (DL)/uplink (UL) subframe structureconsidered in 3GPP LTE-A (LTE-Advanced) system where multiple CCs areaggregated (in this example, 3 carriers exist) is illustrated, a UE canmonitor and receive DL signal/data from multiple DL CCs at the sametime. However, even if a cell is managing N DL CCs, the network mayconfigure a UE with M DL CCs, where M≤N so that the UE's monitoring ofthe DL signal/data is limited to those M DL CCs. In addition, thenetwork may configure L DL CCs as the main DL CCs from which the UEshould monitor/receive DL signal/data with a priority, eitherUE-specifically or cell-specifically, where L≤M≤N. So the UE may supportone or more carriers (Carrier 1 or more Carriers 2 . . . N) according toUE's capability thereof.

A Carrier or a cell may be divided into a primary component carrier(PCC) and a secondary component carrier (SCC) depending on whether ornot they are activated. A PCC is always activated, and an SCC isactivated or deactivated according to particular conditions. That is, aPCell (primary serving cell) is a resource in which the UE initiallyestablishes a connection (or a RRC connection) among several servingcells. The PCell serves as a connection (or RRC connection) forsignaling with respect to a plurality of cells (CCs), and is a specialCC for managing UE context which is connection information related tothe UE. Further, when the PCell (PCC) establishes the connection withthe UE and thus is in an RRC connected mode, the PCC always exists in anactivation state. A SCell (secondary serving cell) is a resourceassigned to the UE other than the PCell (PCC). The SCell is an extendedcarrier for additional resource assignment, etc., in addition to thePCC, and can be divided into an activation state and a deactivationstate. The SCell is initially in the deactivation state. If the SCell isdeactivated, it includes not transmit sounding reference signal (SRS) onthe SCell, not report channel-quality indicator (CQI)/precoding matrixindicator (PMI)/rank indicator (RI)/procedure transaction identifier(PTI) for the SCell, not transmit on UL-SCH on the SCell, not monitorthe PDCCH on the SCell, not monitor the PDCCH for the SCell. The UEreceives an Activation/Deactivation MAC control element in this TTIactivating or deactivating the SCell.

To enhance the user throughput, it is also considered to allowinter-node resource aggregation over more than one eNB/node where a UEmay be configured with more than one carrier groups. It is configuredPCell per each carrier group which particularly may not be deactivated.In other words, PCell per each carrier group may maintain its state toactive all the time once it is configured to a UE. In that case, servingcell index i corresponding to a PCell in a carrier group which does notinclude serving cell index 0 which is a master PCell cannot be used foractivation/deactivation.

More particularly, if serving cell index 0, 1, 2 are configured by onecarrier group whereas serving cell index 3, 4, 5 are configured by theother carrier group in two carrier group scenarios where serving cellindex 0 is PCell and serving cell index 3 is the PCell of the secondcarrier group, then only bits corresponding 1 and 2 are assumed to bevalid for the first carrier group cell activation/deactivation messageswhereas bits corresponding 4 and 5 are assumed to be valid for thesecond carrier group cell activation/deactivation. To make somedistinction between PCell for the first carrier group and the secondcarrier group, the PCell for the second carrier group can be noted asS-PCell hereinafter. Herein, the index of the serving cell may be alogical index determined relatively for each UE, or may be a physicalindex for indicating a cell of a specific frequency band. The CA systemsupports a non-cross carrier scheduling of self-carrier scheduling, orcross carrier scheduling.

FIG. 3 shows a structure of a radio frame to which the present inventionis applied.

Referring to FIG. 3, a radio frame includes 10 subframes, and onesubframe includes two slots. The time taken for one subframe to betransmitted is called a Transmission Time Interval (TTI). For example,the length of one subframe may be 1 ms, and the length of one slot maybe 0.5 ms.

One slot includes a plurality of OFDM symbols in the time domain andincludes a plurality of Resource Blocks (RBs) in the frequency domain.An OFDM symbol is for representing one symbol period because downlinkOFDMA is used in 3GPP LTE system and it may be called an SC-FDMA symbolor a symbol period depending on a multi-access scheme. An RB is aresource allocation unit, and it includes a plurality of contiguoussubcarriers in one slot. The number of OFDM symbols included in one slotmay vary according to the configuration of the CP (Cyclic Prefix). TheCP includes an extended CP and a normal CP. For example, if normal CPcase, the OFDM symbol is composed by 7. If configured by the extendedCP, it includes 6 OFDM symbols in one slot. If the channel status isunstable such as moving at a fast pace UE, the extended CP can beconfigured to reduce an inter-symbol interference. Herein, the structureof the radio frame is only illustrative, and the number of subframesincluded in a radio frame, or the number of slots included in asubframe, and the number of OFDM symbols included in a slot may bechanged in various ways to apply new communication system. Thisinvention has no limitation to adapt to other system by varying thespecific feature and the embodiment of the invention can apply withchangeable manners to a corresponding system.

The downlink slot includes a plurality of OFDM symbols in the timedomain. For example, one downlink slot is illustrated as including 7OFDMA symbols and one Resource Block (RB) is illustrated as including 12subcarriers in the frequency domain, but not limited thereto. Eachelement on the resource grid is called a Resource Element (RE). Oneresource block includes 12×7 (or 6) REs. The number N^(DL) of resourceblocks included in a downlink slot depends on a downlink transmissionbandwidth that is set in a cell. Bandwidths that are taken into accountin LTE are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. If thebandwidths are represented by the number of resource blocks, they are 6,15, 25, 50, 75, and 100, respectively.

The former 0 or 1 or 2 or 3 OFDM symbols of the first slot within thesubframe correspond to a control region to be assigned with a controlchannel, and the remaining OFDM symbols thereof become a data region towhich a physical downlink shared chancel (PDSCH) is allocated. Examplesof downlink control channels include a Physical Control Format IndicatorChannel (PCFICH), a Physical Downlink Control Channel (PDCCH), and aPhysical Hybrid-ARQ Indicator Channel (PHICH).

The PCFICH transmitted in a 1st OFDM symbol of the subframe carries acontrol format indicator (CFI) regarding the number of OFDM symbols(i.e., a size of the control region) used for transmission of controlchannels in the subframe, that is, carries information regarding thenumber of OFDM symbols used for transmission of control channels withinthe subframe. The UE first receives the CFI on the PCFICH, andthereafter monitors the PDCCH.

The PHICH carries acknowledgement (ACK)/not-acknowledgement (NACK)signals in response to an uplink Hybrid Automatic Repeat Request (HARQ).That is, ACK/NACK signals for uplink data that has been transmitted by aUE are transmitted on a PHICH.

A PDCCH (or ePDCCH) is a downlink physical channel, a PDCCH can carryinformation about the resource allocation and transmission format of aDownlink Shared Channel (DL-SCH), information about the resourceallocation of an Uplink Shared Channel (UL-SCH), paging informationabout a Paging Channel (PCH), system information on a DL-SCH,information about the resource allocation of a higher layer controlmessage, such as a random access response transmitted on a PDSCH, a setof transmit power control commands for UEs within a certain UE group,the activation of a Voice over Internet Protocol (VoIP), etc. Aplurality of PDCCHs may be transmitted within the control region, and aUE can monitor a plurality of PDCCHs. The PDCCH is transmitted on oneControl Channel Element (CCE) or on an aggregation of some contiguousCCEs. A CCE is a logical assignment unit for providing a coding rateaccording to the state of a radio channel to a PDCCH. The CCEcorresponds to a plurality of resource element groups (REGs). A formatof the PDCCH and the number of bits of the available PDCCH aredetermined according to a correlation between the number of CCEs and thecoding rate provided by the CCEs.

The wireless communication system of the present invention uses blinddecoding for Physical Downlink Control Channel (PDCCH) detection. Theblind decoding is a scheme in which a desired identifier is de-maskedfrom a CRC of a PDCCH to determine whether the PDCCH is its own channelby performing CRC error checking. An eNB determines a PDCCH formataccording to a Downlink Control Information (DCI) to be transmitted to aUE. Thereafter, the eNB attaches a cyclic redundancy check (CRC) to theDCI, and masks a unique identifier (referred to as a radio networktemporary identifier (RNTI)) to the CRC according to an owner or usageof the PDCCH. For example, if the PDCCH is for a specific UE, a uniqueidentifier (e.g., cell-RNTI (C-RNTI)) of the UE may be masked to theCRC. Alternatively, if the PDCCH is for a paging message, a pagingindicator identifier (e.g., paging-RNTI (e.g., P-RNTI)) may be masked tothe CRC. If the PDCCH is for system information (more specifically, asystem information block (SIB) to be described below), a systeminformation identifier and system information RNTI (e.g., SI-RNTI) maybe masked to the CRC. To indicate a random access response that is aresponse for transmission of a random access preamble of the UE, arandom access-RNTI (e.g., RA-RNTI) may be masked to the CRC.

Thus, the BS determines a PDCCH format according to a Downlink ControlInformation (DCI) to be transmitted to the UE, and attaches a cyclicredundancy check (CRC) to control information. The DCI includes uplinkor downlink scheduling information or includes an uplink transmit (Tx)power control command for arbitrary UE groups. The DCI is differentlyused depending on its format, and it also has a different field that isdefined within the DCI.

Meanwhile, an uplink subframe may be divided into a control region towhich a physical uplink control channel (PUCCH) that carries uplinkcontrol information is allocated; the control information includes anACK/NACK response of downlink transmission. A data region to whichphysical uplink shared channel (PUCCH) that carries user data isallocated in the frequency domain.

The PUCCH may support multiple formats. Namely, it can transmit uplinkcontrol information having different number of bits per subframeaccording to a modulation scheme. PUCCH format 1 is used to transmit ascheduling request (SR), and PUCCH formats 1a and 1b are used totransmit an HARQ ACK/NACK signal. PUCCH format 2 is used to transmit achannel quality indication (CQI), and PUCCH formats 2a and 2b are usedto transmit a CQI and a HARQ ACK/NACK. When an HARQ ACK/NACK istransmitted alone, PUCCH formats 1a and 1b are used, and when an SR istransmitted alone, PUCCH format 1 is used. And PUCCH format 3 may beused for the TDD system, and also the FDD system. PUCCH format 3 can beused to enable the possibility of transmitting more than four bits in anefficient way, even though PUCCH format 3 also be used for transmittingless four bits of signal. The basis of PUCCH format 3 is DFT (DiscreteFourier Transform)-precoded OFDM. Up to five terminals may share thesame resource-block pair for PUCCH format 3 when a length-5 orthogonalsequence is used with each of the five OFDM symbol carrying data in aslot being multiplied by one element of the sequence. A terminal (eNBand/or UE) can be configured with more than one resource (e.g. fourdifferent resources) for PUCCH format 3.

Herein, an ePDCCH can be one of solutions of limitation for a PDCCHtransmission or new control information transmission of near futurecommunication system including a new type of carrier as shown in FIG. 4.

FIG. 4 shows downlink control channels to which the present invention isapplied. The ePDCCH which can be multiplexed with the PDSCH can supportmultiple Scells of the CA.

Referring to FIG. 4, the UE can monitor a plurality of PDCCH/ePDCCHswithin the control region and/or data region. As the PDCCH istransmitted on CCE, ePDCCH can be transmitted on eCCE (enhanced CCE) asan aggregation of some contiguous CCEs, the eCCE corresponds to aplurality of REGs. If ePDCCH is more efficient than PDCCH, it isworthwhile to have subframes where only ePDCCHs are used without PDCCHs.The PDCCHs and new ePDCCH only subframes, or have only ePDCCH onlysubframes can be in a new type of carrier as NC which has both legacyLTE subframes. It is still assumed that MBSFN subframes exist in a newcarrier NC. Whether to use PDCCH in multimedia broadcast singlefrequency network (MBSFN) subframes in NC and how many ODFM symbols willbe allocated if used can be configured via RRC signaling. Further TM10and new TM mode of UE can be considered for new carrier type as well.Hereafter, new carrier type refers to a carrier where all or part oflegacy signals can be omitted or transmitted in different manners. Forexample, a new carrier may refer a carrier where a cell-specific commonreference signal (CRS) may be omitted in some subframes or physicalbroadcast channel (PBCH) may not be transmitted.

FIG. 5 shows an example of dual connectivity to a macro cell and a smallcell. Referring to FIG. 5, the UE is connected to both the macro celland the small cell. A macro cell eNB serving the macro cell may becalled as a MeNB in dual connectivity, and a small cell eNB serving thesmall cell may be called as a SeNB in dual connectivity.

The MeNB is an eNB which terminates at least S1-MME and therefore act asmobility anchor towards the core network (CN) in dual connectivity. If amacro eNB exists, the macro eNB may function as the MeNB, generally. TheSeNB is an eNB providing additional radio resources for the UE, which isnot the MeNB, in dual connectivity. The SeNB may be generally configuredfor transmitting best effort (BE) type traffic, while the MeNB may beresponsible for transmitting other types of traffic such as VoIP,streaming data, or signaling data.

FIG. 6 shows an example of a protocol architecture supporting dualconnectivity. To support dual connectivity, various protocolarchitectures have been studied.

Referring to FIG. 6, PDCP and RLC entities are located in differentnetwork nodes, i.e., PDCP entities in the MeNB and RLC entities in theSeNB. In the UE side, the protocol architecture is same as the prior artexcept that the MAC entity is setup for each eNB (i.e., the MeNB andSeNB).

Meanwhile, a UE may receive signals from more than one cell and transmitsignals to more than one cell under some circumstances. For example, theUE may transmit/receive signal with dual connectivity

In these cases, a small cell can perform “off” and “on” where“off-state” can be defined as a UE may not expect to receive any othersignal except for discovery signals which will be used for cellidentification and/or measurement. It is however noted that othersignals not used for unicast data transmission can still be present. Forexample, positioning reference signal (PRS) or PMCH-related signals canstill be transmitted. In other words, when the cell is OFF,unicast-related signals may not be transmitted including some systeminformation such as SIB and PBCH. The discovery signal may be cellsynchronization/identification signals and/or reference signals formeasurement.

Whether the network transmits other signals or not is up to the network.Yet, a UE do not assume that any other signals will be transmitted inoff-state unless transmitting of other signal besides the discoverysignal configured/indicated/scheduled. Traditionally, a UE may behavebased on assumption that eNB will transmit signals continuously. Thusall the protocols such as discontinuous reception (DRX) and paging arebased on the assumption that eNB can transmit at least reference signalsaccording to UE receiving time.

Now that a cell can turn on and off its transmission, depending on thelevel of turning off, there could be cases where a UE may need to knowthe state of cell-off and thus a UE don't need to expect to receive aset of signals in the off-state.

One example is measurement reference signal (RS) transmission such asCRS where traditionally UE can perform measurement in any subframewhereas, with cell on/off, a UE may be limited to perform measurement ina set of subframes for the measurement or period for the measurement.Otherwise, eNB may need to support those functionalities regardless ofcell state (i.e. on/off state of the cell).

Considering a carrier in unlicensed band in which the network may not beable to transmit continuous CRS, it is assumed that the cell willperform on/off in unlicensed band without any additional information. Itis however notable that a carrier in unlicensed band may indicate thatit will not turn off or it will continuously transmit signals for somereasons. One potential reason is that the channel is idle and the onlydevice utilizing the channel is a LTE eNB. Then, it may indicate it doesnot require turning off the cell and it will be informed to the UE. Whena UE is indicated with this, it can perform measurement/synchronizationcontinuously where the subframes are selected by UE implementation.

The benefit of cell on/off includes both interference reduction andenergy saving. In particular, this invention discusses how to handle eNBdiscontinuous transmission (DTX) and UE DRX effectively.

Overall, from a eNB perspective, four levels (1) to (4) turning off canbe considered.

(1) Total shut off where no signal is transmitted in off state

(2) Synchronization and measurement signal transmission: Such as primarysynchronization signal (PSS)/secondary synchronization signal (SSS)/CRSor discovery signals can be transmitted even in off-state to assist UEmeasurement and cell identification

(3) Transmitting discovery signal+any necessary signals to supportRRC_CONNECTED mode UEs such as DRX, paging: Such as PDCCH aligned withUE DRX cycle or paging data or signals for radio link failure (RLF)related measurement may be sent in off-state to assist RRC_CONNECTEDmode UE functionality. In RRC_CONNECTED, an RRC context is established.That is, a UE knows the cell to which the UE is belongs and the cellknows an identity of the UE, the Cell Radio-Network Temporary Identifier(C-RNTI), used for signaling purposes between the UE and the network.Thus in RRC_CONNECTED mode, data can be transferred to/from the UE, butDRX can be configured in order to reduce terminal power consumption

(4) Transmitting discovery signal+any necessary signals to support bothRRC_CONNECTED and RRC_IDLE mode UEs: In this case, transmission systeminformation/MIB, etc. as well as the signals transmitted in above case(3) are supported. In this case, some services such as D2D(Device-to-device) or MBMS can be also supported. If continuoustransmission of CRS is needed to support such as MBMS, the cell maytransmit CRS continuously. If a subset of signals are needed to supportthose services, those signals are selectively transmitted. In RRC_IDLEmode, no RRC context is established and the UE does not belong to aspecific cell. No data transfer may take place as the UE sleeps most ofthe time. Uplink transmission may be performed to convert move toRRC_CONNECTED.

In addition to above the four levels of turning off (1)-(4), there isanother option to support (3) for advanced UEs and support measurementfor legacy UEs. In this option, measurement signals such as CRS shouldbe also transmitted to support legacy UE measurement.

In this invention, main focus is in option (2) and (3). However, thetechniques proposed here can be applied to other options as well.

It is also further assumed that eNB may or may not turn off receivermodule when it performs DTX. When eNB shuts off the receiver module, itwould be informed to UEs so that UE can stop transmission to the eNB. Ifthere is no signaling, UE may assume that eNB would keep the receivermodule such that UE can transmit uplink signals any time.

UE, however, may not expect to receive downlink signaling correspondingto the uplink signaling. For example, a UE may transmit physical randomaccess channel (PRACH) where random access response (RAR) may not beexpected by the UE when the cell is in off-state. Or, when the cell isin off-state, the latency to acquire response to PRACH may be largerthan the latency currently specified. Alternatively, when there is UEuplink transmission, the network automatically wakes-up and responses toUE uplink transmission.

When a cell performs cell on/off, it is expected that a UE with dualconnectivity or CA capability can be associated with a on/off cell. Interms of signaling whether the cell is on or off, a few mechanisms canbe considered as 1) to 6) as follows.

1) Autonomous detection by UE: A UE may assume that cell is off if CRSand/or PDCCH is not detected at the subframe. Alternatively, a UE candetect predefined signal(s) to indicate the starting time of ON period(such as preamble). When a UE detects the signal, it can assume that thenext T msec, the cell would stay in ON-state. Alternatively, a UE mayhave to detect signal such as CRS or preamble in every subframe todetermine the status of the cell.

2) Based on cell association: A UE may assume that a cell is on-state ifit is associated with the cell. Otherwise, it shall assume that the cellis off. Particularly, for PCell, a UE can assume that the cell isON-state.

3) Based on cell activation: A UE may assume that a cell is on-state ifthe cell is activated. Otherwise, it may assume that the cell is off. Ifthe UE is configured with one or more SCells, the network may activateand deactivate the configured SCells.

The PCell is always activated. The network activates and deactivates theSCell(s) by sending the Activation/Deactivation MAC control element.Furthermore, the UE maintains a sCellDeactivationTimer timer perconfigured SCell and deactivates the associated SCell upon its expiry.

The same initial timer value applies to each instance of thesCellDeactivationTimer and it is configured by RRC. The configuredSCells are initially deactivated upon addition and after a handover.

The UE shall for each TTI and for each configured SCell as below.

If the UE receives an Activation/Deactivation MAC control element inthis TTI activating the SCell, the UE shall be in the TTI according tothe timing defined in 3GPP TS 36.211. To activate the SCell, i.e. applynormal SCell operation including SRS transmissions on the SCell,CQI/PMI/RI/PTI reporting for the SCell, PDCCH monitoring on the SCelland PDCCH monitoring for the SCell. Start or restart thesCellDeactivationTimer associated with the SCell;

Else, if the UE receives an Activation/Deactivation MAC control elementin this TTI deactivating the SCell.

Or if the sCellDeactivationTimer associated with the activated SCellexpires in this TTI. In the TTI, the Scell is deactivated, thesCellDeactivationTimer associated with the SCell is stopped, all HARQbuffers associated with the SCell is flushed.

If PDCCH on the activated SCell indicates an uplink grant or downlinkassignment; or

If PDCCH on the Serving Cell scheduling the activated SCell indicates anuplink grant or a downlink assignment for the activated SCell. ThesCellDeactivationTimer associated with the SCell is restarted.

If the SCell is deactivated, SRS on the SCell is not transmitted,CQI/PMI/RI/PTI for the SCell are not reported, UL-SCH on the SCell arenot transmitted on, the PDCCH on the SCell is not monitored, the PDCCHfor the SCell is not monitored.

4) Based on explicit signaling: A UE may assume that a cell is on or offbased on explicit signaling. One example is to introduce a new MAC CE orRRC signaling to indicate the transition of cell state (from off to onor vice versa). Similar to cell activation/deactivation, MAC CEsignaling can be introduced to indicate the state of the cell. Uponreceiving the MAC CE to indicate cell ON-state, a UE can assume that thecell will be in ON-state until OFF-state indication is received. Anotherexample is to use dynamic signaling such as DCI to indicate whether thecell state has changed or not. In case that explicit signaling has beenmissed, a UE may assume that a predetermined set of subframes are ON andother subframes are OFF. For that, either via SIB or RRC signaling, afallback ON-subframes can be configured.

5) Based on cell ID or discovery signals: If a cell uses differentdiscovery signals or IDs per a state (that is a different IDs for onstate and off state), by detecting its ID or signals, a UE can determinethe state of the cell. Upon detecting “on-state” discovery signals, a UEmay assume that it can attempt to read data channels.

6) Based on DRX configuration: A UE may assume that a cell is on-stateonly in “active state” per DRX configuration.

Except for 6), there could be cases where a UE is configured with DRXcycle where the cell is in off-state. How to handle this case, we canconsider a few approaches such as (i)-(v) as follows.

(i) DRX cycle always has higher priority over cell on/off state. Inother words, a UE can expect to receive PDCCH/PDSCHs in active-state ofeach DRX cycle. A UE will monitor active state per DRX protocol to seewhether any data has been transmitted.

(ii) DRX cycle is effective only when the cell is on-state. In thiscase, in active-state of a DRX cycle, if a UE knows that the cell isoff-state, it knows that any transmission would not be occurred. Sothat, it is not required to monitor PDCCH/PDSCHs in those subframes. DRXcycle and timers will not be changed. Only, the UE is not required tomonitor PDCCH/PDSCHs in the subframes where the cell is off-state withactive-state per DRX cycle.

(iii) DRX is not configured with on/off cell. In this case, a UE shallignore any configured DRX cycle for a cell performing cell on/off eventhough it is configured with a DRX cycle. If a UE is configured withPCell and SCell where SCell performs cell on/off, DRX applies only toPCell. This is particularly useful in case where the UE does not knowthe state of the cell. Yet, it needs to know whether the cell canperform on/off or not. The information where the cell performs on/offcan be configured to a UE via measurement configuration or by otherhigher layer signaling. When a cell changes its state from on/off cellsto always-on cells, the information may be reconfigured or updated.

This option is particularly useful for unlicensed band carrier as a UEmay not be able to find any signal during DRX OFF and also inonDuration, a UE may not be able to find any signal to receive (E)PDCCH.To handle this issue, a UE may assume that DRX configuration (ifconfigured) is not applicable to unlicensed band carrier(s). It mayassume that it does not need to monitor downlink channels by theconfiguration only.

(iv) Whether to use DRX in SCell or assisting eNB can be configured. Ifconfigured to be used, a UE is allowed to operate DRX. In this option,depending on UE knowledge on cell state or not, it can be furtherassumed that a UE ignore DRX on-duration if the cell is in off-state.Or, if it is configured, UE may assume that DRX operation is supportedby the cell.

(v) If a UE supports CA or dual connectivity, it can be assumed that aUE shall monitor PDCCH in PCell for SCell DRX as well where PDSCH/PUSCHcan be transmitted via SCell performing on/off using cross-CCscheduling. If a UE supports cross-CC scheduling, a UE may behigher-layer configured to monitor PCell or macro eNB PDCCH in DRXactive-state for SCell DRX cycle based on cross-layer scheduling. Thisapproach would be useful as it does not mandate cell on/off performingcell to transmit PDCCHs in off-state to support DRX cycle of UEs. Yet,if the cell is active state which is not known to UE before, thesignaling can be transmitted via PCell/macro eNB. In this case, bothPCell and SCell (or macro eNB and assisting eNB) transmit PDCCH and onlySCell (or assisting eNB) transmits PDSCH at least a few subframes toavoid a case where a UE does not detect PDCCHs in PCell. When a UEdetects PDCCH scheduled to itself using cross-subframe scheduling, itstarts to run inactivityTimer to decide when to go back to DRX and alsoit starts monitoring PDCCH on SCell.

This option would be useful for unlicensed band carrier. Instead of notapplying DRX cycle in unlicensed band, it can also apply DRX inunlicensed band whereas it should not assume that signals will bepresent in DRX onDuration or activeTime in unlicensed band carrieritself. In this case, onDuration/PDCCH may be monitored only vialicensed band carrier(s) such as via PCell—some description isillustrated in FIG. 7. This may be applied even if self-scheduling isconfigured for unlicensed band carrier.

FIG. 7 describes an example of case (v) above. In the example of FIG. 7,PCell transmits PDCCHs always where PDCCHs for SCell PDSCH/PUSCH can betransmitted in PCell as well. A UE, once detecting PDCCH in on-state,may monitor SCell PDCCHs starting the next subframe.

Alternatively, a DCI transmitted in PCell may be used as an indicator ofSCell activity. Once the DCI indicates SCell becomes active, the UEshall start monitoring on SCell.

(vi) UE DRX aligned with cell DTX: In this example, all UEs associatedwith a cell may be configured with one DRX cycle which is aligned withcell DTX cycle. In the DTX cycle, a UE can monitor PDCCHs in on-durationwhere the timer reset could be somewhat different from UE-specific DRXas it is a cell-specific DTX cycle. To determine whether on-durationcontinues or not, a UE may detect either CRS or PDCCH with a new RNTI(such as CELL-ON-RNTI) or PDCCH with C-RNTI.

If a UE detects PDCCH with a new RNTI, it may assume that a cell will beactive until inactivityTimer expires. This new RNTI can be cell-specificor group-specific which will be higher layer configured. If a UE detectsthe activity of a cell based on CRS, the reliability may be decreasedand there could be mis-alignment among UEs. To minimize the impact,on-duration should be at least a few msec where a UE will have at leasta few opportunities to detect CRS or PDCCH. To allow a UE withmis-alignment between DRX and DTX, a UE without receiving valid CRS orPDCCH for a duration (such as MaxCellOffTime) may assume it ismisaligned and indicates the state to the PCell or macro eNB or triggerRLF.

This option could be used in unlicensed band carrier to indicate dynamicon/off operation or discontinuous transmission. It is based on UE blinddetection on such as CRS/PDCCH to determine the status of the carrierwith a higher layer configured OFF time which can be mapped to back-offduration or idle time between transmissions. When an eNB needs to followEU regulation, it needs to wait a certain time before the nexttransmission where no transmission would be occurred. Thus, DRX/DTXcycle can be configured along with that constraint where the cell willtransmit signals if channel is acquired based on Listen-Before-Talk(LBT). If this is supported, it may be necessary to configure separateDRX configuration between licensed and unlicensed carrier groups.

Regardless which options used, a UE shall assume that a cell inoff-state or when a UE is in DRX state, it should not expect to receiveany signal except for discovery signaling (cellsynchronization/identification signals and/or measurement signals) andother necessary signals such as PMCH, D2D related signals and PRS.

To handle paging, also, similar approaches can be possible where pagingcan be delivered to on/off cells or paging can be handled by PCell orother Scell which is not performing cell on/off or the cell with RRCconnection. If a cell performing on/off has at least one associated UEwhich is not capable of CA or dual connectivity, the cell eithersupports paging regardless of cell state or it may disable paging in asystem in this case limited functionality is supported for earthquakeand tsunami warning system (ETWS) or Community Modeling and Analysis(CMAS) and thus it may not associate UEs supporting those applications.Furthermore, it could be also desirable not to support UEs without CA ordual connectivity capability. Furthermore, if the paging is supported, anew paging cycle can be also considered which can be aligned with cellon/off period.

Assuming a discovery signal can be used for UE measurement, in terms ofUE behavior on measurement can be categorized such as (A) and (B) below.

(A) UE measurement always based on discovery signals: Regardless of cellstate, UE shall perform radio resource management (RRM) measurementbased on discovery signals. In terms of CSI measurement, if PMI-RI-off,it shall assume that CRS is available in subframes configured to measureCSI. For example, when CSI0 is used for measurement, CSI0 carries CRS.

(B) UE measurement using discovery signal only when cell is noton-state: If a UE knows the state of the cell, it can use theinformation to enhance the measurement accuracy. For example, ifactivation/deactivation based cell on/off is used, the UE knows thatactivated SCell and/or PCell is ON-state. In that case, a UE can uselegacy CRS for its measurement on activated SCell and/or PCell.

It is also possible that whether a UE use only discovery signals for itsmeasurement or can use legacy measurement signals on on-state of thecell (or to the neighbor measurement as well) can be configurable. Onemechanism of configuration is to configure a list of cells withdiscovery signals for its measurement such that other cells outside ofthe cell ID list may be based on legacy signals. Or, if it isconfigured, a UE shall report two types of measurement when a cell ison-state. For a neighbor cell, unless configured otherwise,discovery-signal based measurement is assumed. If configured, a UE mayreport additional report based on legacy signals such as PSS/SSS/CRS.

For stand-alone ON/OFF operation, the following operations may beconsidered.

Radio Link Monitoring

The current requirement on radio link monitoring is as follows: Innon-DRX mode operation, the physical layer in the UE shall assess theradio link quality for every radio frame, evaluated over the previoustime period defined in 3GPP TS 36.321, 36.101 or 36.104 (hereinafter,3GPP TS 36.321, 36.101 or 36.104 are called as “the references” in thisapplication) against thresholds (Q_(out) and Q_(in)) defined by relevanttests in references. In DRX mode operation, the physical layer in the UEshall assess the radio link quality at least once every DRX period,evaluated over the previous time period defined in the references,against thresholds (Q_(out) and Q_(in)) defined by relevant tests in thereferences. If higher-layer signalling indicates certain subframes forrestricted radio link monitoring, the radio link quality shall not bemonitored in any subframe other than those indicated. The physical layerin the UE shall in radio frames where the radio link quality is assessedto indicate out-of-sync to higher layers when the radio link quality isworse than the threshold Q_(out). When the radio link quality is betterthan the threshold Q_(in), the physical layer in the UE shall in radioframes where the radio link quality is assessed to indicate in-sync.

If this requirement is kept, if a UE is not configured with DRX and thenthe cell can be off, either eNB may inform UE the state so that therequirement changes to one of three alternatives alt1 to alt3 as below.

Alt1 (if a UE knows the state). In non-DRX mode operation and also thecell is not in off-state, the physical layer in the UE shall assess theradio link quality per every radio frame, evaluated over the previoustime period defined in the references, against thresholds (Q_(out) andQ_(in)) defined by relevant tests in the references.

Alt2 (RLM can be configured). If a UE is configured to perform radiolink monitoring (RLM) and in non-DRX mode operation, the physical layerin the UE shall assess the radio link quality per every radio frame,evaluated over the previous time period defined in [10], againstthresholds (Q_(out) and Q_(in)) defined by relevant tests in thereferences. In this case, it is assumed that all subframes in non-DRXmode are ON-state.

Alt3 (RLM subframe can be configured). In non-DRX mode operation and insubframes configured to perform radio link monitoring, the physicallayer in the UE shall assess the radio link quality per every radioframe, evaluated over the previous time period defined in [10], againstthresholds (Q_(out) and Q_(in)) defined by relevant tests in thereferences.

If a UE can be configured with DRX, and some of options listed in thisinvention applies and then a UE is configured or required to performradio link monitoring on the cell which performs cell on/off, one of theoptions (A) to (F) may be used as below.

For DRX, if option (A) may be used: In DRX mode operation, the physicallayer in the UE shall assess the radio link quality at least once everyDRX period, evaluated over the previous time period defined in thereferences, against thresholds (Q_(out) and Q_(in)) defined by relevanttests in the references.

For DRX, if option (B) may be used: In DRX mode operation, the physicallayer in the UE shall assess the radio link quality if a cell ison-state at least once every DRX period, evaluated over the previoustime period defined in the references, against thresholds (Q_(out) andQ_(in)) defined by relevant tests in the references.

Note that period can be changed to count only DRX episodes where thecell were on-states only. Thus, the latency can be changed if the cellperforms cell on/off and can be increased if cell performs frequenton/off.

For DRX, if option (C) may be used: In DRX mode operation, UE ignoresDRX mode operation and perform radio link monitoring per non-DRX modeoperation.

For DRX, if option (D) is used: In DRX mode operation, if a UE isconfigured with enabled DRX mode operation in the cell, follow in DRXmode operation such as (a) or (b) otherwise (c) as below.

(a) In DRX mode operation, the physical layer in the UE shall assess theradio link quality at least once every DRX period, evaluated over theprevious time period defined in the references, against thresholds(Q_(out) and Q_(in)) defined by relevant tests in the references.

(b) In DRX mode operation, the physical layer in the UE shall assess theradio link quality at least once every DRX period if a cell is on-state,evaluated over the previous time period defined in the references,against thresholds (Q_(out) and Q_(in)) defined by relevant tests in thereferences.

(c) In DRX mode operation, UE ignores DRX mode operation and performradio link monitoring per non-DRX mode operation.

For DRX, if option (E) may be used: In DRX mode operation, the physicallayer in the UE shall assess the radio link quality at least once everyDRX period if the cell is active, evaluated over the previous timeperiod defined in the references, against thresholds (Q_(out) andQ_(in)) defined by relevant tests in the references. Or, in DRX modeoperation, the physical layer in the UE may not perform radio linkmonitoring.

For DRX, if option (F) may be used: In DRX mode operation, the physicallayer in the UE may not perform radio link monitoring.

Alternatively, radio link monitoring may be performed solely based ondiscovery signals and measurement signals which can be transmitted inoff and on state.

Also, if a UE is configured with DRX and it knows that the cell mayperform cell on/off, it assumes that in DRX operation and DRX cycle inwhich the cell may not transmit measurement signals. Thus, it should notassume that it can perform measurement in any time. The guaranteedmeasurement subframes would be subframes carrying discovery andmeasurement signals transmitted in off-state (as well as in on-state)and/or signals in on-state.

Also, if a UE knows that the cell may perform on/off, it may not bemandated to monitor PDCCH in every subframe. Rather, if a UE knows theactive state by either activating the cell or associating the cell, itshould assume that PDCCH monitoring is mandated only in subframesconfigured to do so.

CRS Transmission in ON-State with/without Data Transmission

As it may not be necessary to transmit CRS in certain subframes such assubframes with demodulation reference signals (DM-RS), furtheroptimization to reduce CRS transmission in small cell can be considered.With multiple configurations, a UE per each subframe may determinewhether CRS is going to be transmitted or not based on the followingconfigurations.

(1) If a UE is not configured with DRX or the current subframe per DRXconfiguration is OnDuration (i.e., active subframe):

A. If a UE is configured with EPDCCH and the current subframe is notpart of EPDCCH monitoring subframe set (i.e., PDCCH monitoringsubframe), then a UE shall assume CRS will be present at least first twoOFDM symbols.

i. If a UE is configured with CRS-based transmission mode: If thecurrent subframe is not MBSFN subframe per configuration, UE shallassume that CRS will be present throughout the whole subframe.Otherwise, it shall assume only first two OFDM symbols will carry CRS.

ii. If a UE is configured with DM-RS based transmission mode, if thecurrent subframe is not part of restricted measurement subframe set, itshall assume only first two OFDM symbols will carry CRS. If it doesbelong to the restricted measurement subframe set, UE shall assume thatCRS will be present throughout the whole subframe

B. If a UE is configured with EPDCCH and the current subframe is part ofEPDCCH monitoring subframe set,

i. If a UE expects to receive common-search-space DCI or P-RNTI,SI-RNTI, RA-RNTI, scrambled DCI in the current subframe, it shall assumeat least first two OFDM symbols will carry CRS.

ii. If a UE is configured with CRS-based transmission mode: If thecurrent subframe is not MBSFN subframe per configuration, UE shallassume that CRS will be present at least in PDSCH region.

iii. If a UE is configured with DM-RS based transmission mode, if thecurrent subframe belongs to the restricted measurement subframe set, UEshall assume that CRS will be present throughout the whole subframe

(2) If a UE is configured with DRX and the current subframe per DRXconfiguration is not OnDuration (i.e., active subframe): A UE shall notassume CRS will be present in the subframe.

(3) In other cases, a UE shall not assume CRS will be present in acertain OFDM symbol or subframe.

For unlicensed band carrier, it can be assumed that CRS will betransmitted in a subset of subframes where one or a few followingconditions i.e. {circle around (a)}-{circle around (f)} as below aresatisfied.

{circle around (a)} A UE is configured with CRS-based transmission modeand the subframe is not configured as MBSFN subframe.

{circle around (b)} A UE is configured with monitoring PDCCH in thatsubframe

{circle around (c)} A UE is configured to decode PMCH for the servingcell

{circle around (d)} A UE is configured to receive D2D relatedconfiguration from the serving cell

{circle around (e)} The subframe is part of DRS subframes

{circle around (f)} The subframe is configured by higher layer assubframe to carry CRS

Activation/Deactivation of SCell Process with Cell on/Off

When a cell is turned on or off via SCell activation/deactivationcommand, we can slightly change the timing of SCellactivation/deactivation to aid cell on/off procedure.

If a UE is configured with fast cell activation/deactivation (such asvia FastCellOnOffActivated is configured as TRUE), a UE shall assume thefollowings: When a UE receives an activation command the references fora secondary cell in subframe n, the corresponding actions in thereferences shall be applied no later than the minimum requirementdefined in [10], and no earlier than the latency T configured by higherlayer, except for the following two actions {circle around (1)} and{circle around (2)}. {circle around (1)} The actions related to CSIreporting and {circle around (2)} the actions related to thesCellDeactivationTimer associated with the secondary cell the referenceswhich shall be applied in subframe n+T (n is integer). Note that if T isnot configured, default value should be 8. Also note that T should belarger than 8. If small number is configured, UE shall ignore theconfiguration and set T as T=8. Note that if T is larger than theminimum requirement defined in the references, T has higher priority andthus activation will occur no earlier than T. When a UE receives adeactivation command the references for a secondary cell or thesCellDeactivationTimer associated with the secondary cell expires insubframe n, the corresponding actions in the references shall apply insubframe n, including CSI reporting.

The motivation of having higher layer configured value of T is to allowcell wake-up procedure occurred via backhaul procedure where backhauldelay can be larger than 8 msec (MAC CE delay) which could be inaddition to MAC CE delay. The reason of “instantaneous” deactivation isto allow fast turn off procedure of a small cell.

Activation/Deactivation of Super SCell Process with Cell on/Off

When attaching assisting eNB via activation/deactivation procedure, toaddress backhaul latency, deactivation message may also carry latencyvalue. Different from activation/deactivation procedure listed above,when a UE is deactivated, a UE may also be configured with latency Twhich may be shared between activation and also deactivation. If latencyis applied for deactivation procedure as well, the procedure would be asthe following: When a UE receives a deactivation command the referencesfor a secondary cell or the sCellDeactivationTimer associated with thesecondary cell expires in subframe n (n is integer), the correspondingactions in the references shall apply in subframe n+T where T is higherlayer configured latency value including CSI reporting.

By this means, SeNB may reserve cell off and turn off the cellimmediately at the reserved time.

Physical Multicast Channel (PMCH) Reception

A UE shall not assume that eNB may transmit CRS and/or PDCCH insubframes where PMCH reception is occurred unless the carrier isactivated as a SCell or super SCell or PCell. In other words, a UE shallnot assume that PDCCH/CRS will be transmitted in MBSFN subframes unlessthe cell is activated and serving cell.

In this case, a UE may still assume that subframes carrying MBMS-relatedSIBs (such as SIB1/2, SIB13) may transmit CRS/PDCCH. Furthermore, sincetracking is needed, transmission of tracking signals such as CRS isassumed as well.

More specifically, not to change the UE behaviour, it can be assumedthat if a network indicates the intention of MBMS service in a frequencyby a cell, a UE can expect that cells supporting MBMS in that frequencywill not turn off. Thus, a UE can expect reading legacy signals fromthat cell.

This is particularly important even in case of discovery signalmeasurement is configured. Even if discovery signal measurement isconfigured, it is expected that a UE can assume the cell is maintainingON state if the cell indicates MBMS service. Thus, a UE can expectsignals from the cell. In other words, a UE can expect that the cellmaintains ON-state if it is configured by higher layer to decode PMCHfor the cell even though the cell is deactivated SCell.

Similarly, for device-to-device (D2D) operation, if a network indicatesD2D operation in that frequency, a UE may assume that the network willnot perform cell on/off regardless of cell activation/deactivation.Thus, a UE can assume certain signals in case of D2D operation isconfigured by the cell.

It is however notable that unlicensed band, even with MBMS, CRS/PDCCHtransmission may not be assumed. Rather, MBMS-related configuration maybe delivered via PCell or licensed carrier instead of acquiring fromunlicensed band carrier itself. It is also notable that MBMS service canbe occurred in any subframe regardless of MBSFN configuration inunlicensed band carrier.

MBSFN Configuration

Now that a cell may perform on/off operation, during off-state, a cellmay be able to utilize all subframes as MBSFN subframes for MBMS. Thus,MBSFN subframe configuration can be extended to cover all subframes in aradio frame. At least off-state or unlicensed band carrier, allsubframes could be used for MBMS transmission. From a UE perspective,when a carrier is activated, all subframes may not be usable for MBSFNsubframes.

In this case, additional MBSFN subframe configuration can be configuredvia higher layer signaling if necessary.

Otherwise, UE may assume that subframe #0/#4/#5/#9 in FDD are reservedfor downlink data transmission or CRS transmission or UE may assume thatsubframe #0/#5 in FDD are reserved for CRS transmission and thus thosereserved subframes may not be usable for MBSFN subframes when thecarrier is activated even though MBSFN subframe configuration via SIB orhigher layer signaling indicates otherwise.

For TDD, subframe #0/#1/#5/#6 may be reserved for CRS or subframe #0/#5may be reserved for potential CRS transmission. Moreover, a UE mayassume that subframes configured for discovery signal transmission arenot MBSFN subframes regardless of MBSFN configuration. Optionally MBSFNsubframe configuration can be omitted in such case a UE may assume thatall subframes can be used for MBSFN subframes when cell is off-state.

Disco Very Signal Scrambling Sequence

To allow super dense small cell environment, it is desirable to increasethe number of cell IDs in a hierarchical fashion such as cluster ID andcell ID may be used jointly. For example, instead of 10 bits of cell ID,14 bits of ID can be used where cluster ID (4 bits)+cell ID (10 bits)can be used.

The intention is to create unique ID from any UE perspective and alsofrom the network perspective. It is important to have a unique ID fromthe network perspective as well since a UE may report measurementresults based on ID and the network should be able to differentiatecells which may have the same cell ID due to the lack of pre-planningvia separating clusters.

In other words, cell ID can be used within a cluster and cluster ID canbe used across the clusters to assign unique IDs. This is particularlyimportant with cell on/off scenarios where cells are densely deployedand use the same cell ID for UE-centric virtual cell formation. Also,discovery signal may be transmitted to UEs without knowledge of subframenumber or SFN, thus, scrambling may be occurred without slot or subframeor radio frame number. One example of scrambling sequence initializationusing CSI-RS for discovery signal is as MTH 1c _(init)=2¹⁰·(7·(N _(ID) ^(ClusterI)+1)+/+1)·(2·N _(D) ^(CSI)+1)+2·N_(D) ^(CSI) +N _(CP)  <MATH 1>

Consideration of Explicit Indication of Cell ON/OFF

When explicit signalling is used, some issues related to periodicity andfallback issue need to be considered. For example, explicit signallingcan be transmitted every 5 msec/10 msec at a set of fixed subframes(such as subframe #0, #5).

Explicit DCI can be transmitted via cross-carrier scheduling from PCellfor example, or self-scheduling from SCell. If cell-common DCI is used,it would be good to utilize cell-common search space (CSS), thus, it canbe considered to assume cross-carrier scheduling from PCell.

When ON/OFF indication DCI is missing, it is necessary to define afallback behaviour. One simple approach is to assume that all subframesare “OFF” if valid DCI has not been successfully detected at a givenindication subframe. Another approach is to assume all subframes are“ON”. Alternatively, it can be assumed that a set of subframes areassumed to be “ON” regardless of ON/OFF operation/DCI.

When ON/OFF indication is sent from PCell, it is necessary to containthe information of SCell information. One approach is to include cell IDand the bitmap of ON/OFF pattern, or a mapping between ON/OFF indicationDCI to a cell needs to be defined. Similar to enhanced interferencemanagement and traffic adaptation (eIMTA), it can be also considerablethat ON/OFF can be applied for multiple carriers, and thus, ON/OFFindication per carrier can use 1 or 2 bits per each carrier where themapping between the order of ON/OFF indication DCI (which containsON/OFF indication for multiple carriers) and the cell can be configuredby higher layer.

If bitmap is used, four bits of bitmap can be considered if periodicityof ON/OFF indication is transmitted in every 5 msec where subframe #0/#5may be assumed as “ON” regardless of ON/OFF indication. Four bits foreach carrier which can perform ON/OFF can be sent via a DCI.

Even in case of DCI missing, a UE may still assume that PHICH-expectedsubframes are “ON”-subframes. In unlicensed band, a UE may assume thatall subframes are potentially OFF. When a UE sends PUSCH, thecorresponding downlink subframe (PHICH-subframe) is assumed as ONsubframe regardless of ON/OFF indication.

If a set of predetermined/higher layer configured subframes is assumedto be “ON” regardless of ON/OFF indication, the UE may perform RRMmeasurements only in those subframes unless configured otherwise viarestricted measurement or other means such as discovery signals.Furthermore, it can be also assumed that RLM is performed in thosesubframes only unless configured otherwise.

FIG. 8 is a flowchart briefly describing an example of operation of a UEaccording to the invention(s) in this application.

Referring to FIG. 8, the UE receives signal from a cell on downlinkchannel at step S810. Here, the cell may perform cell on-off. When thecell is in off-state, the UE may receive signal including discoverysignal from the cell.

The UE may determine whether the cell is in off-state or in on-stateusing one of the methods described before. When the UE determined thatthe cell is in off-state, the UE may process on the signal (e.g.discovery signal) in consideration that the cell is in off-state.

The received signals, the determination and assumption as to cell on/offand process considering cell on/off were described in tail.

The UE transmits signal on uplink channel at step S820. The UE maytransmit signal based on the determination as to whether the cell is inoff-state or not. The detailed descriptions as to this are same asprovided before.

FIG. 9 is a flowchart briefly describing an example of operation of aeNB (BS) according to the invention(s) in this application.

Referring to FIG. 9, the eNB receives signal from a UE on uplink channelat step S910. Here, the eNB may perform cell on/off. The eNB may receivesignals such as reports on measurement with reference signal from theUE.

However, the cell may be in off-state.

The eNB transmit signals to the UE on downlink channel at step S920.When the eNB is in off-state, the eNB may transmit signal underpredetermined condition as described before. The eNB may notice itsstate (i.e. in off-state or in on-state) to the UE by signalling or thestate of the eNB may be indicated to the UE by blind detection. Inaddition, the signal from the eNB in off-state may be restricted insignalling type, signalling timing, channel to be transmitted, number ofsignalling, information in the signal, etc. The details are same asdescribed before.

FIG. 10 is a block diagram which briefly describes a wirelesscommunication system including an UE 1000 and a BS (eNB) 1040. The UE1000 and the BS 1040 may operate based on the description as explainedabove.

In view of downlink, a transmitter may be a part of the BS 1040 and areceiver may be a part of the UE 1000. In view of uplink, a transmittermay be a part of the UE 1000 and a receiver may be a part of the BS1040.

Referring to FIG. 10, the UE 1000 may include a processor 1010, a memory1020 and a radio frequency (RF) unit 1030.

The processor 1010 may be configured to implement proposed proceduresand/or methods described in this application. For example, the processor1010 may determine whether the BS (cell) is in off-state or in on-statebased on signals, blind detection, etc. The processor 1010 may performmeasurement under consideration that the BS may be in off-state. Thedetailed description on the processor 1010 is the same in much of theoperation of the UE described above.

The memory 1020 is coupled with the processor 1010 and stores a varietyof information to operate the processor 1010, which includes datainformation and/or control information.

The RF unit 1030 is also coupled with the processor 1010. The RF unit1030 may transmit and/or receive a radio signal. The signal may includea discovery signal when the signal is transmitted from the eNB inoff-state.

The BS 1040 may include a processor 1050, a memory 1060 and a RF unit1070. Here, the BS may be PCell or SCell and the BS may be a macro cellor small cell. In addition the BS may be a source cell for networksynchronization or a target cell for network synchronization.

The processor 1050 may be configured to implement proposed proceduresand/or methods described in this application. For example, the processor1050 may perform cell on/off. The processor 1050 may transmit/receivesignal under certain condition when the eNB (cell) is in off-state. Forexample, the eNB may transmit a discovery signal only when the eNB is inoff-state. The details are already described before in this application.

The memory 1060 is coupled with the processor 1050 and stores a varietyof information to operate the processor 1050, which includes datainformation and/or control information. The RF unit 1070 is also coupledwith the processor 1050. The RF unit 1070 may transmit and/or receive aradio signal. The signals transmitted or received via the RF unit 1070are also described before.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, the above-described embodiments include variousaspects of examples. Accordingly, the present invention should beconstrued to include all other alternations, modifications, and changeswhich fall within the scope of the claims.

In the description regarding the present invention, when it is said thatone element is “connected” or “coupled” to the other element, the oneelement may be directly connected or coupled to the other element, butit should be understood that a third element may exist between the twoelements. In contrast, when it is said that one element is “directlyconnected” or “directly coupled” to the other element, it should beunderstood that a third element does not exist between the two elements.

The invention claimed is:
 1. A method for communicating with a smallcell, which supports an on-state and an off-state, and a macro cell in awireless system, the method performed by a user equipment (UE) andcomprising: receiving, from the small cell, a discovery signal includingan identification which indicates whether the small cell is in theon-state or the off-state; determining whether the small cell is in theon-state or the off-state based on the identification; and performing adiscontinuous reception (DRX) operation based on the determined state ofthe small cell, wherein when the identification indicates that the smallcell is in the on-state, the UE performs measurement using a cellspecific reference signal (CRS), and wherein when the identificationindicates that the small cell is in the off-state, the UE only receivesthe discovery signal, performs measurement using the discovery signal,and performs the DRX operation by aligning a cycle of the DRX operationwith a cycle of the on-state of the small cell and the off-state of thesmall cell.
 2. The method of claim 1, wherein when the small cell isdeactivated, the small cell is in the off-state.
 3. The method of claim1, wherein the UE determines that the small cell is in the on-state whenthe UE receives multimedia broadcast/multicast service (MBMS) from thesmall cell.
 4. The method of claim 1, wherein the UE further receivessupporting information being information supporting a radio resourcecontrol (RRC) connection of the UE, and wherein the supportinginformation includes information for the DRX operation.
 5. A userequipment (UE) communicating with a small cell, which supports anon-state and an off-state, and a macro cell in a wireless system, the UEcomprising: a radio frequency (RF) transceiver that transmits andreceives a signal; and a processor, operatively coupled to the RFtransceiver, that: controls the RF transceiver to receive, from thesmall cell, a discovery signal including an identification whichindicates whether the small cell is in the on-state or the off-state,determines whether the small cell is in the on-state or the off-statebased on the identification, and performs a discontinuous reception(DRX) operation based on the determined state of the small cell, whereinwhen the identification indicates that the small cell is in theon-state, the UE performs measurement using a cell specific referencesignal (CRS), and wherein when the identification indicates that thesmall cell is in the off-state, the UE only receives the discoverysignal, performs measurement using the discovery signal, and performsthe DRX operation by aligning a cycle of the DRX operation with a cycleof the on-state of the small cell and the off-state of the small cell.6. The UE of claim 5, wherein when the small cell is deactivated, thesmall cell is in the off-state.
 7. The UE of claim 5, wherein whetherthe small cell is in the on-state or the off-state is determined by theprocessor based on explicit signaling or higher layer signaling.
 8. TheUE of claim 5, wherein the processor determines that the small cell isin the on-state when the RF transceiver receives multimediabroadcast/multicast service (MBMS) from the small cell.
 9. The UE ofclaim 5, wherein the processor further controls the RF transceiver toreceive supporting information being information supporting a radioresource control (RRC) connection of the UE, and wherein the supportinginformation includes information for the DRX operation.